This invention relates generally to data rendering methods to enhance the image quality for volumetric 3D displays, particularly for displaying color or gray scale images on volumetric 3D displays using image sources with binary pixels. A volumetric 3D display displays 3D images in a real 3D space. Each “voxel” in a volumetric image locates actually and physically at the spatial position where it is supposed to be, and light rays travel directly from that position toward omni-directions to form a real image in the eyes of viewers. As a result, a volumetric display possesses all major elements in both physiological and psychological depth cues and allows 360° walk-around viewing by multiple viewers without the need of special glasses.
One typical category of volumetric 3D (V3D) displays generates V3D images by moving a screen to sweep a volume and projecting 2D images on the screen. V3D images thus form in the swept volume by after-mage effect. The screen motion can in general be rotating or reciprocating. Tsao U.S. Pat. No. 6,765,566 B1 describes a system with a screen that reciprocates by a rotary motion. (See FIG. 20 of the referred patent) In principle, this is to revolve the screen about an axis and sweep a volume while keeping the screen surface always facing a fixed direction. For convenience, this is called “Rotary Reciprocating mechanism”. In Tsao U.S. Pat. No. 6,302,542, a volumetric 3D display with a Rotary Reciprocating screen and a Rotary Reciprocating reflector serving as a linear interfacing unit is described. (See FIGS. 2a, 4b and 5b and the specification of the referred patent) The Rotary Reciprocating reflector reciprocates by a similar Rotary Reciprocating mechanism in synchronization with the screen but at a speed of ½ of the speed of the screen. FIG. 1 illustrates such a V3D display system, in side view. It has three major portions: a rotary reciprocating screen unit 1511 (comprising a screen 11 mounted on rotary arms 1522); a high frame rate image projection system 15; and an optical interfacing mechanism 13 (comprising a single reflector 1321 mounted on rotary arms 1322). A stationary reflector 1502 folds the projection path. The set of rotary arms 1322 and the set of rotary arm 1522 rotate synchronously. The figure shows the screen at the top position. When the screen rotates to the bottom position 11A, the interfacing reflector rotates to position 1321A The projection path is from the projector 15 to the interfacing reflector 1321, then to the folding reflector 1502 and then to the screen. This projection path length is kept constant as the screen and the interfacing reflector rotate. Projection path 402 strikes the interfacing reflector 1321 at an oblique angle, therefore the sides of the resulted display volume 12 are of the shape of parallelogram. The high-frame-rate projector projects a set of 2D image frames onto the moving screen. The moving screen moves and therefore distributes the 2D image frames to corresponding positions in the space swept by the screen. Together, the spatially distributed 2D images form a volumetric 3D image.
In the above example of volumetric 3D display, the preferred image source for the projector is DMD (Digital Micro-mirror Device) or FLCD (Ferroelectric Liquid Crystal Display). These are devices of black and white pixels. Using a single DMD or FLCD with a white or monochrome light results in a monochrome volumetric 3D display.
To create colors, one can use three DMDs or FLCDs, each illuminated by light of a different primary color. Alternatively, Tsao U.S. patent application Ser. No. 09/882,826 (2001) describes a method of using a single panel to generate colors. The single panel is divided into 3 sub-panels and each sub-panel is illuminated by light of a different primary color. The images of the 3 sub-panels are then recombined into one at projection. However, because each pixel has only two levels (black and white), the combination of three panels or sub-panels can only generate limited amount of colors.
Such limitation on gray scale and color exists on many other types of V3D displays, as long as they are based on binary image sources.
Presenting levels of gray scale (or intensity or brightness) is important in image display. The capability of presenting high gray scale is the fundamental for presenting high level of colors, because colors are formed by mixing of a limited number of primary colors and gray scale capability also determines the brightness level of each of the primary colors. Gray scale presentation is also one major issue in displaying biomedical data, as medical imaging instrument such as X-ray CT scanner creates images of scales of intensity.
Therefore, methods must be devised to break this hardware limitation.
Tsao U.S. Pat. No. 6,765,566 describes a data processing method for volumetric 3D display including a step of converting a set of raw 3D data into a Viewable Data, which comprises three basic geometric forms: scattered points, curves (including lines) and surfaces. Scattered points can be used to render a surface or the interior of a region. Curves can be used to represent, in addition to curves, surfaces. And surfaces can be used to represents, in addition to surfaces, volumes bounded by them. Viewable Data of the three basic forms is then processed into a set of Displayable Data using various color combination methods. The Displayable Data can then be used to generate the optical image patterns to be projected and recombined and displayed in the volumetric 3D display. Tsao also describes a method of rendering a surface with color or gray scale by stacking closely multiple layers of sub-surfaces, each of a different primary color but a similar shape, called “color sub-surfaces” method.
This invention is to further develop the method of using scattered points for rendering lines, surfaces and volumes, in order to display volumetric 3D images with high level of colors or gray scales in space.
This invention is to provide a detailed algorithm of using scattered points to render a solid triangular surface of gray scale by controlling the size and the density of the scattered points. (Called “Simple Rendering”, see Sec. 4.1 in Detailed Description)
This invention is also to provide a detailed algorithm for rendering a solid triangular surface with color or gray scale based on the “color sub-surfaces” method. This algorithm combines three basic controls to create high level of colors/gray scales: point size control, point density control and multiple sub-surfaces. (Called “Multi-layer Rendering” in Sec. 4.2)
This invention is also to provide the principle and the algorithm for rendering a surface with a given bitmap texture. This texture-mapping algorithm also combines the use of the three basic controls. This allows a volumetric 3D display based on binary pixels to display texture mapped surfaces with reasonable presentation of color or gray scale distribution and without sacrificing resolution. (See Sec. 5 Texture Mapping)
This invention is also to provide the principle and the algorithm of using points to render a 3D volume with distributed gray scale (or a similar property), by controlling the size and the density distribution of the scattered points. (Called “Voxel Mapping” in chapter 6) This allows a volumetric 3D display based on binary pixels to display 3D volume data with reasonable presentation of color or gray scale distribution and without sacrificing resolution.